Modern integrated circuit IC devices typically employ shallow trench isolation and multi-level interconnects to meet the demands for increased functionality and faster processing speeds. However, planarization of interlevel dielectrics, conductive layers and trench dielectrics are required when using these technologies to obtain optimum fabrication results.
One technique that provides planarization and has received widespread acceptance in the semiconductor processing industry is chemical-mechanical polishing CMP.
CMP is used to planarize and remove surface topography irregularities of a material layer through chemical reaction and mechanical abrasion.
Typically a CMP process involves placing a semiconductive substrate (e.g. a semiconductive wafer) face down on a polishing pad where the polishing pad is attached to a rotatable table, or platen. An abrasive fluid, known as slurry, is introduced onto the surface of the polishing pad while the polishing pad is being rotated and the substrate is pressed against the polishing surface of the polishing pad. Additionally, the substrate may also be rotated in conjunction with the rotating polishing pad.
The polishing of the substrate by the chemical mechanical process is provided by chemical interaction of the slurry, which includes a chemical reagent, with the substrate and abrasives contained within the slurry, where typical abrasives used in the CMP include silica, alumina and ceria. However, other abrasives may be used.
The polishing process starts with the chemical interaction between the slurry and the substrate (i.e. material layer) with the abrasives in the slurry, coupled with the rotational movement of the polishing pad, physically stripping the reacted surface material from the substrate. The polishing process continues until the desired amount of the material layer is removed. Upon completion of the polishing process the substrate is subjected to a cleaning process to remove residual slurry and foreign particles.
However, by semiconductor fabrication standards CMP is inherently a dirty process, which in addition to a significant amount of foreign particles being introduced to the substrate surface also results in a significant amount of foreign particles, for example abrasive particles and by products of the planerization, being introduced to the polishing pad that can result in an undesirable built up of particles on the polishing pad, which is an effect known as ‘pad glazing’.
Pad glazing results in the smoothing of the upper surface (i.e. working surface) of the polishing pad causing a reduction in the abrasive properties of the polishing pad and consequently a reduction in the polishing rate. Additionally, the ‘glaze’ is often unevenly distributed over a polishing pad surface, which can result in localized differences in polishing rate and increased polishing non-uniformity.
One way to alleviate this problem has been via the use of a conditioning device that is used to remove the ‘glaze’ and other unwanted particles from the polishing pad.
The technique of conditioning the polishing pad with a conditioning device involves mechanically abrading the polishing pad surface to remove the glaze and ‘renew’ the polishing pad surface.
The conditioning surface of a conditioning device typically includes an abrasive surface, for example diamonds, to provide the mechanical abrasion. During pad conditioning the conditioning device, for example a diamond disk, is positioned over the polishing pad and a downward force applied such that the conditioning surface of the conditioning device is in abrasive contact with the polishing surface. The conditioning device may sweep back and forth across the surface of the polishing pad, which may be rotated, to facilitate removal of the glaze across the surface of the polishing pad. A rinsing fluid, for example deionised water, is typically injected onto the polishing pad to aid in the removal of abraded glaze from the polishing pad surface. However, it has been found that the use of a chemical reagent in place of the deionised water helps reduce the accumulated glaze on the polishing pad.
However, it has been found that abrasive particles and by products generated as a result of the polishing process can be transferred from the polishing pad onto the conditioning device resulting in a build up of a film, comprising unwanted particles, on the conditioning device.
As a result of a film build-up on the conditioning device the conditioning capabilities of the conditioning disk are reduced resulting in a lower removal rate of unwanted particles from the polishing pad by the conditioning device and less uniform conditioning of the polishing pad by the conditioning device.
This problem is further exacerbated in that there are no convenient means of monitoring the condition of the conditioning device and consequently the current solution to this problem is to change the conditioning disk on a regular basis rather than when the conditioning device is determined to be no longer suitable for conditioning of a polishing pad.
It is desirable to improve this situation.